A standard flow-control a valve has a rotary spindle that must be turned through at most 360.degree. between a full-on and a full-off position, and a stem surrounding the spindle. This stem is normally faceted, that is of polygonal shape and is centered on the rotation axis of the spindle. The spindle also is normally formed with teeth so that it can be fitted to a actuator for rotation of it and operation of the valve. For manual operation a handle with a seat complementary to the spindle is fitted to the spindle.
It is also known to provide such a standard rotary valve with a motorized actuator so that it can be operated remotely, and to provide in the actuator some form of sensor so that the position of the valve can be detected remotely. The typical motor actuator is a complex item that cannot readily be mounted on a standard flow-control valve. Even if some adapter can be used to mount the actuator to a normally manual valve, adjustment of it and of its angular position detector is a complex job.